Terry has designed broadcast stations, recording studios, broadcast equipment, intelligent machines and special computer languages for IBM, and has worked as a broadcast journalist covering elections, fires, riots and Woodstock.
He has taught electronics

Cool. Like to see people digging way below the usual detail level of Arduino into the Atmel reality.

Fantasy: At some Ultrasonic frequency there are TWO outputs of this type. But the PHASE between those can be varied and they drive two separate Ultrasonic transducers. There is one (maybe 2?) Ultrasonic transducer receivers. Some kind of Phased Array technique allows not just distance but some spatial location information to be recovered from object(s) in front of the array. Maybe.

About that Word: I used to give some little talk called "Fantasy as an Engineering Design Tool" which was actually well received, even by Software types. I once told a meeting at Perkin-Elmer Corp. that they had "A really nice Fantasy about this Deep-UV technique being applied to chip lithography". They were a little miffed. But later a couple guys told me they really understood, and that they fought with Management which wanted them to "Stop the Blue Sky Stuff" and Get To Work.

One great thing about Arduino is that most of us are not doing this stuff At Work...

Fantasy: At some Ultrasonic frequency there are TWO outputs of this type. But the PHASE between those can be varied and they drive two separate Ultrasonic transducers. There is one (maybe 2?) Ultrasonic transducer receivers. Some kind of Phased Array technique allows not just distance but some spatial location information to be recovered from object(s) in front of the array. Maybe.

With the toneAC library you can also connect two piezo/speakers that will generate out of phase signals. On the Uno, one tied to 9 and GND and the other tied to 10 and GND. Both will produce the same frequency. Not sure what exactly the volume (duty) will do. If it will adjust the duty for each equally or opposite of each other.

One great thing about Arduino is that most of us are not doing this stuff At Work...

I'm trying to change that. We have a new overhead audio marketing division and I'm trying to do the full design from hardware to software. The difference in price from commercial options for hardware are making my proposal very interesting to the owner. I can envision moving all my Arduino stuff out of my house and converting my office to a "tinker shed". My wife would also appreciate it to get her house back.